Accommodating additional data on an optical data carrier disk

ABSTRACT

An optical data carrier disk reader is adapted for detecting a slope of a wall in a data track of an optical disk. An optical disk has pits ( 811, 812 ), having walls with at least two different steepnesses, in its data track. The steepness represents information written on the optical disk. A method for making an optical disk stamper ( 8 ) comprising exposing portions of a photo-sensitive layer to electro-magnetic radiation is also described. By controlling the variation of the focal point during exposure, the inclination of the walls between the bump ( 811, 812 ) or pit forming portions and the “land” forming portions of the surface of the optical disk stamper ( 8 ) can be controlled.

The invention relates to an optical disk reader device, to a method formaking an optical disk stamper, to an optical disk, to a controllerdevice, to a computer program, and to a data storage device.

In general, optical disk reader devices read data from optical diskssuch as a compact disk (CD) or a digital versatile disk (DVD).

It is an object of the invention to store more data on an opticaldigital data carrier disk and to be able to read more data from suchdisks.

For storing more data, according to one aspect of the present invention,an optical disk according to claim 1 is provided. For reading such adisk, an optical disk reader according to claim 5, a method according toclaim 7 and a computer program according to claim 11 are provided. Formanufacturing a stamper from which such a disk can be manufactured, theinvention provides a method according to claim 8.

Specific embodiments of the invention are set forth in the dependentclaims.

Further details, aspects and embodiments of the invention will bedescribed with reference to the attached drawings.

FIG. 1 schematically shows a cross-section along a data track of anexample of an optical disk according to the invention.

FIG. 2 schematically shows an example of an optical disk readerapparatus according to the invention

FIG. 3 schematically shows a reader device for in the optical diskreader of FIG. 2.

FIG. 4 shows a graph of the simulated reflection of laser radiation onan optical disk according to the invention as a function of time

FIG. 5 shows a graph of the tangential push-pull signal on an opticaldisk according to the invention as a function derived from thereflection of FIG. 4.

FIGS. 6-10 show exploded, perspective views of several stages of anexample of a method for making an optical disk stamper according to theinvention.

The example of an optical disk 7 according to the invention shown inFIG. 1 comprises a base layer 71, a reflective layer 72 with areflective boundary 68 and a protection layer 73. Seen from a readingside 76 of the disk, the reflective layer 72 has bumps 75. Of course,seen from the other side, the bumps are pits. The bumps project from abase level 77 to a bump level 69. The area of the reflective layer atthis level is the “pit” 78. The bumps 75 represent data written on theoptical disk and constitute a spiral data track, which is denoted with79 in FIG. 2.

In use, the optical disk 7 may be read from the reading side 76 byprojecting a laser radiation beam onto the disk and detecting the amountof reflected radiation at a sensor. In the shown example, the height hover which the bumps 75 project from the land 78 is around or at aquarter of the wavelength of the projected radiation. When the diskrotates, the radiation reflected to the sensor from the lands hastraveled ¼+¼=½ of a wavelength further than radiation reflected from thebumps 75. The radiation reflected from the land is therefore shifted by½ a wavelength relative to light (visible or invisible) reflected fromthe bumps and is thus out of phase with the radiation reflected from thebumps. Thus, if a bump 75 is present in the light beam, the lightreflected from the bump cancels out light reflected from the land, sothat no or substantially less radiation is reflected to the sensor. Ifthe beam hits land only, no interference occurs.

In the present context the planes of the base level 77 and the bumplevel are denoted as horizontal planes and the orientation perpendicularthereto is denoted as vertical.

The bumps 75 have walls 74, 74′ with different slopes (in this context,a vertical wall is also regarded as having a slope). For example, someof the walls 74 are substantially vertical, while other ones of thewalls 74′ are less steep. Thus, there are several types of walls on thedisk which can be distinguished from each other by the steepness of thewalls. This distinction can be used to store data on the disk. Therebyan extra data channel is provided. The data channel may for example beused to increase the data density of the disk or for copyrightprotection. The extra data channel is independent of the informationrepresented by the bumps and does not influence the behavior of the diskin conventional optical disk readers which are not capable ofdistinguishing walls of different steepness from each other. Thus, theextra data channel is fully backward compatible.

Furthermore, the extra information stored in the slopes or steepnessesof the walls sloping in the direction of the data track cannot easily becopied from the optical disk onto another optical disk disk for tworeasons. Firstly, the known optical data readers do not output theinformation on the extra channel, so obtaining the data in the extradata-channel would require a modification to the optical disk readerhardware. Secondly, writable optical disks, such as rewritable CD's, donot have a bump structure, so it is not possible to store informationonto the walls of the bumps in such types of disks.

FIG. 2 schematically shows an example of an optical disk reader 1according to the invention. The shown reader 1 can for example be acompact disk (CD) reader or a digital versatile disk (DVD) reader. Thereader 1 comprises a reader unit 2 for directing a light beam 2′ to thedisk 7 and for sensing light reflected from the disk 7 and a datacarrier holder 3. The reader unit 2 and the data carrier holder 3 aremovable with respect to each other in a conventional manner as indicatedby arrows A′,A″,A′″. The data carrier holder 3 holds the optical disk 7in position with respect to the reader unit 2.

The data carrier holder 3 and the disk 7 carried thereby can be rotatedby a motor 32 about an imaginary axis 31, as indicated in FIG. 2 byarrow A. The reader unit 2 is mounted on a sledge 4 and movable withrespect thereto in the direction indicated by arrow A″. The sledge 4 ismovable in the directions indicated by arrow A′ (perpendicular todirections indicated by arrows A″ and A′″) by sliding the sledge 4 overgliders 5. The movement of the reader unit 2 and the sledge 4 is drivenby one or more suitable actuators, for instance electro motors, whichare not shown in the drawing and well known in the art. The distancebetween the reader unit 2 and the optical disk 7 is also adjustable,because the reader unit 2 is also movable with respect to the opticaldisk 7 in the direction indicated with arrow A′″

The reader unit 2, the sledge 4, the motor 32 and the actuators areconnected to a control circuit 6, which may be connected to otherdevices and/or circuits inside or outside the data reader device via acontrol terminal 63. The control circuit 6 may perform variousfunctions. One of these functions is processing signals from or to thereader unit 2. Other functions may for example be control of therotational speed of the motor 32 and optical disk 7, control of anactuator which moves the sledge or the reader unit 2. In FIG. 2, thecontrol circuit 6 is depicted as a single unit, however, the device mayphysically be distributed over separate units.

Data may be read from bit positions on the data track 79 using thereader unit 2. By rotating the holder 3 the optical disk 7 is rotatedwith respect to the reader unit 2. The reader device 2 can be moved in aradial direction with respect to the imaginary axis 31 by moving thereader unit 2 with respect to the sledge 4 and/or moving the sledge 4along the gliders 5. Thus, data may be read by the reader unit 2 fromthe track 79 of the optical disk 7.

In the shown example, the reader unit 2 directs a laser beam indicatedin FIG. 2 by dotted line 2′ to the disk 7. The laser beam 2′ isgenerated by a laser source and focused on the optical disk 7 by anobjective lens. The laser source and the lens are part of the readerunit 2 and are not shown in FIG. 2. The laser beam 2′ is reflected bythe optical disk 7 and detected by the reader unit 2.

The reader unit 2 is provided with means for determining the slope ofwalls on the optical disk 7. The determined slope may then be convertedinto a data signal. For example if the slope is determined to be below acertain threshold value, if may be regarded as a binary zero and if theinclination of the wall is above the threshold it may be regarded as abinary one.

The reader device 2 may be implemented as is shown in FIG. 3. In FIG. 3,a laser source 29, for example a laser diode, is located in line with anoptical system 28, which, in use, projects laser radiation from thelaser source onto an optical disk 7 and directs reflected radiation to aset of detectors 21-24.

The detectors 21-24 output the read data as well as one or more signalsindicative of the position of the reader unit 2 with respect to the datatrack 79 of the optical disk 7. The signal can also form a feedbacksignal in response to a signal sent by the reader unit 2 to the datacarrier device 3.

The optical system 28 comprises a diffraction grating 281, whichprojects radiation through a beam splitter 282 and a collimator lens 283onto a quarter wave length plate 284. The plate 284 transmits theradiation onto an objective lens 285 which focuses the radiation onto anoptical disk 7.

In use, the grating 281 converts the radiation into a central peak plusside peaks. These three beams pass through the polarizing beam splitter282. The splitter transmits polarizations parallel to the plane of thedrawing. The emerging radiation, now polarized parallel to the plane ofthe drawing, is then collimated by the collimator lens 283.

The collimated radiation goes through the ¼ wave plate 284. The plate284 converts the collimated radiation into circularly polarizedradiation. The circularly polarized radiation is then focused down ontothe disk 7 by the objective lens 285. If the radiation strikes “land” itis reflected back into the objective lens. If part of the radiationstrikes a bump, that part cancels out reflection from the “land” becauseof the interference, as is described above with reference to FIG. 1.

After reflection, the radiation passes through the ¼ wave plate again284. Since it is going the reverse direction, it is polarizedperpendicular to the original beam (i.e. perpendicular to the plane ofthe drawing). When the polarized return radiation hits the polarizingbeam splitter 282, it is reflected to the lens system 27 and nottransmitted through the beam splitter 282, the radiation then reflectsthrough a focusing lens 271 and a cylindrical lens 272 of the lenssystem 27 and is imaged on the detector arrangement 21-24.

The presence of bumps on the optical disk 7 is detected by the detectorsin the detector array simply by the presence or absence of reflectedradiation at any of the detectors. The inclination of the walls may bedetected using differences between the detectors. For example, the tiltof the walls influences the tangential push-pull (TPP) signal, which isthe signal representing differences in quantity of radiation betweenleading and trailing halves (leading and trailing being determined inthe direction of progress of the disk with respect to the point ofincidence of the radiation beam) of the reflected radiation incident ondetectors 21-24. Thus the TPP signal is a measure for the tangentialspeed of the effects on the optical disk, i.e. the speed of thedatatrack 79.

When a radiation beam passes across a bump 75, initially only theleading half of the light beam is positioned on the bump 75 and finallyonly the trailing part of the beam in directed to the bump 75.Therefore, intensity distribution of the reflected radiation varies withthe progress of the beam across a bump. Therefore, a pulse-shaped signalforming the tangential push-pull signal is obtained, which representsthe difference at a moment when the radiation beam reaches a bump orleaves a bump, that is, at an edge of the bump, if the wall is vertical.If the inclination of the wall is less steep, the TPP signal will beshaped differently. Difference shown in FIG. 5

Thus, the TPP is a measure of the inclination of the walls of the bumpson the optical disk In FIG. 3, the detectors 21-24 are connected tofirst and second operational amplifiers or opamps 61,62. The detectors,which may for example be photo-diodes, are connected to each other bypairs. Each pair 21,23;22,24 is formed by the detectors which arelocated side-by-side with respect to arrow B, which correspond to thedirection of movement of the bumps with respect to the reader unit 2.The first opamp 61 outputs the TPP signal, while the second opamp 62outputs the data signal related to the presence of the bumps as such.The first opamp 61 compares the signal at the input+with the signal atthe input−and outputs a signal relating to the difference between thesignals, thus determining the difference in intensity of laser radiationimpinging on the pairs of detectors.

Detection of information can be carried out by monitoring the highfrequency content of the TPP signal at the zero crossings of the normalHF signal, i.e. the reflected laser radiation. Since the TPP signal isalready made available in virtually all optical disk readers, existingoptical disk reader electronics designs require little adaptation toenable the readout of the extra information contained in the differencesof steepness of the walls of the bumps.

In the graphs of FIGS. 4-5, the results of a simulation which shows thetotal signal and the TPP signals is depicted. In the simulation, tworuns were made, one where all walls have the same slope and one wherethe bumps causing signal portions 47 and 49 were simulated to have anangle of 50 degrees, and where all other bumps still have walls having aslope of 55 degrees.

In the graph of FIG. 4, both total reflected radiation signals areplotted that resulted from both runs. As is seen, there is virtually nodifference in the signals between the two runs.

In FIG. 5. the corresponding TPP signals are shown. The solid linerepresents the run where the walls have an angle of 55 degrees for allof the bumps, the dash-dotted line is the case where the slope of thewalls for the bumps causing the pulses indicated with 47 and 49 waschanged from 55 to 50 degrees. At the zero crossings of the signal, i.e.the moments the reflected signal crosses line Z, the difference betweenthe TPP signals of both runs is most evident. The simulations shows thatthe change of the slope angles of the pits does not change the qualityof the reflected radiation signal and there is only a small increase injitter.

In FIGS.6-8 a stamper 8 for manufacturing optical data carrier disksaccording to the invention is shown in successive stages of a method formaking the stamper. FIG. 6 shows a glass plate 80 with a photo-sensitivelayer 81 which is exposed to laser radiation. At places where pits (forforming bumps in the disk) have to be created, the laser radiation isprojected. Where land has to be created, the laser radiation is notprojected onto the photosensitive layer. By changing the focal point ofthe radiation, the depth profile of the laser radiation is adjusted. Asthe laser moves along the surface in the direction indicated with arrowC, the focal point is changed. The depth in the photosensitive layer ofthe focal point determines the inclination of the wall of the pit whichis formed, as is illustrated by in FIG. 6 at points N and O.

As shown in FIG. 7, after exposure, the photo-sensitive layer hasexposed portions 811, 812 with leading and trailing boundaries havingdifferent slopes. After exposure, the photo-sensitive layer 81 isdeveloped. Thereby, the photo-sensitive layer is removed at exposedparts, resulting in gaps in the layer 81, as is shown in FIG. 8. Next,the developed layer 81 is covered with a stamper layer 82. In moststamper manufacturing processes the stamper layer 82 is a metal layer.Next, the glass plate 80 and the layer 81 are separated from the stamperlayer 82 and the stamper is obtained using the stamper layer 82. As isshown in FIG. 10, the stamper 82 has bumps 811, 812 having walls withdifferent slopes.

The invention is not limited to implementation in the disclosed examplesof devices, but can likewise be applied in other devices. In particular,the invention is not limited to physical devices but can also be appliedin logical devices of a more abstract kind or in a computer programwhich enables a computer to perform functions of an optical disk readeraccording to the invention or a method according to the invention whenrun on the computer. Furthermore, the leading and trailing walls neednot be straight from the base level to the bump or pit level, but canfor instance be stepped, concave or convex. Instead of by the steepnessof the walls, the distinction between the walls of different categoriescan be made by distinguishing walls of different shape.

1. An optical data carrier disk (7) having an optically reflectiveboundary (68) determining a base level (77) and including a data track(79) readable by an optical disk reader, said data track (79) includinga succession of at least pits or bumps (75) in said boundary (68), saidpits or bumps each having a boundary portion on a pit or, respectively,bump level (69) different from said base level and boundary portionsforming leading and trailing walls (74, 74′) interconnecting said pitor, respectively, bump level boundary portions with boundary portions onsaid base level (77) and forming leading and, respectively, trailingends of pits or, respectively, bumps (75), said walls each having asteepness and each belonging to one of at least two wall categories,walls (74) of a first one of said wall categories having a first slopeand walls (74′) of a second one of said wall categories having a secondslope different from said first slope.
 2. An optical disk (7) as claimedin claim 1, wherein said first slope differs from said second slope bythe average steepness from the base level (77) to the pit level or thebump level (69).
 3. An optical disk (7) as claimed in claim 2, whereinsaid first slope and said second slope have substantially the sameshape.
 4. An optical disk (7) as claimed in claim 1, wherein said walls(74, 74′) of said first and second categories each have a substantiallyconstant steepness from the base level (77) to the pit level or the bumplevel (69).
 5. An optical disk reader (1) for reading data from anoptical data carrier disk (7), said disk reader having a disk holder (3)and a reading assembly (2) including means for directing a light beamonto successive portions of a data track (79) in a reflective boundary(68) of said disk (7) passed by said reading assembly (2), a sensor forsensing variations in light reflected from said boundary (68) caused bya succession of at least pits or bumps (75) in said data track (79) andmeans for generating a signal from said light variations and outputtingsaid signal, said signal corresponding to said succession of at leastpits or bumps (75) in said data track (79), further including means fordetecting and distinguishing variations in reflected light caused byleading and trailing walls (74, 74′) of said pits or bumps of a firstwall category having a first slope from variations in said reflectedlight caused by leading and trailing walls (74′) of said pits or bumpsof a second wall category having a second slope different from saidfirst slope, said means for generating a signal from said lightvariations being adapted for generating and outputting said signal or afurther signal in accordance to detected and distinguished walls (74,74′) of said first and second wall categories in said data track (79).6. An optical disk reader (1) as claimed in claim 5, wherein saidreading assembly (2) comprises: at least two photo-electrical sensors(21, 23 and 22, 24), each for generating a signal in response toelectro-magnetic radiation impinging thereon, the first one of saidphoto-electrical sensors being positioned to receive light reflectedfrom a portion of said light beam leading in the direction of progressalong said data track (79) and the second one of said photo-electricalsensors being positioned to receive light reflected from a portion ofsaid light beam trailing in the direction of progress along said datatrack (79), and subtractor means (61) connected to the first and secondphoto-electrical sensors (21, 23 and 22, 24) for generating a signalrepresenting the difference in intensity between light detected by saidfirst photo-electrical sensor (21, 23 or 22, 24) and light detected bysaid second photo-electrical sensor (22, 24 or 21, 23).
 7. A method forreading data from an optical data carrier disk (7), comprising: passinga successive portions of a data track (79) including a succession of atleast pits or bumps (75) in an optically reflective boundary (68) of anoptical data carrier disk (7) through a light beam (2′), sensingintensities of light reflected from said boundary (68) including saidsuccession of at least pits or bumps (75) in said data track (79), andgenerating a signal from said light variations and outputting saidsignal, said signal corresponding to said succession of at least pits orbumps (75) in said data track (79), wherein intensities of reflectedlight caused by leading and trailing walls (74, 74′) of said pits orbumps are detected, and wherein a portion of said intensities caused byleading and trailing walls (74, 74′) of a first wall category having afirst slope are distinguished from another portion of said intensitiescaused by leading and trailing walls (74′) of a second wall categoryhaving a second slope different from said first slope, and wherein saidsignal or a further signal is generated and outputted in accordance todetected and distinguished walls (74, 74′) of said first and second wallcategories in said data track (79).
 8. A method for manufacturing astamper for manufacturing optical data carrier disks, comprisingexposing successive portions (811, 812) of a data track trajectory in aphoto-sensitive layer (81) to one of a beam of electromagnetic radiationand a beam of particles, said beam having a focal point (N, O) locatedin said photo-sensitive layer (81); varying the depth of said focalpoint (N, O) with progress along said data track trajectory; developingsaid photo-sensitive layer (81); covering said developed photo-sensitivelayer (81) with a stamper layer (82) and separating said developedphoto-sensitive layer (81) from said stamper layer (82).
 9. A method asclaimed in claim 8, wherein said beam is selectively switched on and offwith and without varying the depth of said focal point (N, O) withprogress along said data track trajectory, such that walls of exposedportions (811; 812) of said photo-sensitive layer (81) with differentslopes are obtained.
 10. A method as claimed in claim 8, wherein therate of variation of the depth of the focal point per unit of progressalong said data track trajectory is selectively varied, such that wallsof exposed portions (811; 812) of said photo-sensitive layer (81) withdifferent slopes are obtained.
 11. A computer program for controlling adata processor for interpreting a signal from a reading assemblycorresponding to variations in light intensity of light reflected froman optical data carrier disk, comprising: instructions for reading asignal representing the intensity of light reflected from said boundary(68) including said succession of at least pits or bumps (75) in saiddata track (79), instructions for generating a signal from said lightintensities and for outputting said signal, said signal corresponding tosaid succession of at least pits or bumps (75) in said data track (79),instructions for reading detected intensities in reflected light causedby leading and trailing walls (74, 74′) of said pits or bumps,instructions for distinguishing detected intensities caused by leadingand trailing walls (74, 74′) of a first wall category having a firstslope from detected intensities caused by leading and trailing walls(74′) of a second wall category having a second slope different fromsaid first slope, and instructions for generating and outputting thesignal or a further signal in accordance to detected and distinguishedwalls (74, 74′) of said first and second wall categories in said datatrack (79).
 12. A digital data carrier including data representing acomputer program as claimed in claim 11.